Move backup from one local storage to another

This week, I’ll be switching my local backup storage from a USB hard drive to a NAS. I’m guessing the best (or at least fastest) way to migrate and continue revising my existing backup would be to rsync the whole backup directory to the NAS. Is this correct? What steps would I follow in the web GUI to point the backup ID to the new storage location after the files have copied?

Separate but related question: On the advice of the good people here, I’m also planning to switch from IDrive to Storj. Currently I have IDrive set up to be copy-compatible with the local backup. Can I still set a different chunk size when I set up Storj, or is that something I would’ve had to specify when I set up the local storage?

Yes

Delete the old destination on a local USB drive, and add a new one pointing to the NAS (sftp, smb, etc), with the same name as the old one.

You can have copy-compatible storages with different chunk sizes; but this only controls how chunks will be created during backup. If you do duplicacy copy from existing storage the chunks will not get resized.